Sand molds and cores are conventionally employed in the foundry industry for the production of precision castings. These mold or cores are generally composed of sand particles bonded together with a resin binder.
A wide variety of techniques have been developed for the manufacture of sand molds. Generally, these techniques involve the use of thermosetting acid hardenable resin binders for the sand particles in order to form molds or cores having the requisite surface hardness smoothness, strength and gas permeability so as to produce precision castings.
One method which has found widespread use in producing sand molds and cores involves heating a patterned mixture of sand and a thermosetting resin at a temperature generally ranging from 300.degree. F. to 600.degree. F. for a period of time sufficient to melt or polymerize the resin and therefore produce the desired mold or core (i.e. the hot-box or shell methods). Such processes are described by Brown et al, U.S. Pat. No. 3,020,609 and Dunn et al, U.S. Pat. No. 3,059,297 (each of which is incorporated herein by reference in its entirety).
A particular disadvantage of the so called "shell" method resides in the high cost of the resin coated sand needed. Furthermore, both the shell and hot-box methods require heating of the pattern boxes to temperatures of from 300.degree. F. to 600.degree. F. for periods of time which results in a considerable consumption of energy and fuel which with todays ever growing energy crisis renders such techniques economically unattractive.
More recently, methods have been devised which eliminate the necessity of polymerizing the sand/resin mixture at elevated temperatures. These new methods, commonly referred to as 37 no-bake" or "cold-box" techniques, generally involve the use of an acid catalyst to polymerize the sand/thermosetting resin mixture. The acid catalyst may be in liquid, solid or gaseous form. Such processes are described by Blaies, U.S. Pat. No. 3,008,205; Dunn et al, U.S. Pat. No. 3,059,297; Peters et al, U.S. Pat. No. 3,108,340; Kottke et al, U.S. Pat. No. 3,145,438; Brown et al, U.S. Pat. No. 3,184,814; Robins, U.S. Pat. No. 3,639,654; Australian Pat. No. 453,160 and British Pat. No. 1,225,984, the entire contents of each of the foregoing being incorporated herein by reference in its entirety. Many of these processes involve the use of sulfur containing acid catalysts such as benzene sulfonic acid, toluene sulfonic acid and the like.
When using the "no-bake" or "cold-box" methods, foundrymen generally find the resulting mold or core to exhibit a low tensile strength, thereby necessitating the use of undesirably high amounts of resin to attain satisfactory strength and core hardness. Use of higher such amounts of resin is not only costly but provides a less satisfactory casting.
While such "no-bake" or "cold-box" methods provide a more efficient means of producing sand molds and cores, there is ever present the desirability of increasing the tensile strength and core hardness of such products. Likewise, in view of the relatively short cure time of some sand/resin/acid catalyst systems, it is desirable to increase the working time (i.e. mixing, mulling and depositing in mold or core forming cavity) of the sand/resin/catalyst mix.
In addition, some difficulty has been experienced by foundrymen in maintaining good steel strength qualities with precision steel castings made from sand molds or cores produced using a sulfur containing catalyst. With a no-bake process using a sulfur free catalyst steel strength is no problem.
Accordingly, it is the primary object of the present invention to overcome some of the aforementioned difficulties and provide a means for increasing the tensile strength and core hardness of sand molds and cores.
It is also an object of the present invention to provide a means for increasing the working time of sand/resin/catalyst mixes used in the formation of sand molds and cores.
A further object of the present invention is to provide new sulfur-free catalyst and resin materials for the production of sand molds or cores useful in providing precision steel castings free of sulfur defects.
Still a further object of our invention is to provide sand molds and cores having enhanced strength and core hardness.
These and other objects of our invention will be more apparent from the discussion which follows.